1. Field of the Invention
The present invention relates to editing original video data of a first format, wherein said first format has inserted jitter frames and is displayable at a first frame rate.
2. Description of the Related Art
It is well known that commercial video systems operate at thirty frames per second, slightly less than thirty frames per second (NTSC drop frame) or twenty-five frames per second; rates determined primarily by the frequency of AC mains supplies. It is also well known that high quality cinematographic film is displayed at twenty-four frames per second, therefore there is an inherent difficulty in terms of converting film images into video data.
A process of 2:3 insertion for converting from twenty-four frames per second to thirty frames per second is well known and results in five output frames being generated from four input frames on a repeating cycle. Input frames making up the cycle are usually referred to as A, B, C and D frames from which five output frames are generated. A further complication with commercial video systems is that each frame is generated from two interlaced fields therefore it is more correct to think in terms of generating ten output fields from four input frames.
The known 3:2 insertion process generates three output frames that are derived from a whole input frame. However, in addition to this, two frames are constructed in which interlaced fields are derived from different input frames such that when viewed as a still frame, there is a tendency for the image to jitter, particularly if movement has occurred between the two source frames.
After 3:2 inserted video material has been produced, it may be necessary to perform post production activities resulting in material being modified. In order to do this, the inserted video is reconverted back into material at twenty-four frames per second whereafter (theoretically) edits could occur at any frame boundary. However, given that material must be written back to an inserted video stream, known systems only allow edits at the boundaries between a D Frame and an A Frame, that is to say, at the start of the insertion cycle. Consequently, material that has been processed in this way introduces a further limitation into the editing process which may result in artistic compromises being made or may result in the introduction of artefacts.